SPECTROSCOPIC ANALYSIS OF HOT, HYDROGEN-RICH WHITE DWARFS: THE PRESENCE OF METALS AND THE BALMER-LINE PROBLEM

Journal Article · Wed Sep 01 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/720/1/581· OSTI ID:21460101

Gianninas, A; Bergeron, P ^[1]; Dupuis, J ^[2]

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1. Departement de Physique, Universite de Montreal, C.P. 6128, Succ. Centre-Ville, Montreal, Quebec H3C 3J7 (Canada)
2. Canadian Space Agency, 6767 Route de l'Aeroport, Longueuil, Quebec J3Y 8Y9 (Canada)

We present an analysis of optical spectra for 29 DAO white dwarfs. First, we present our new up-to-date model atmosphere grids computed without the assumption of local thermodynamic equilibrium in which we have included carbon, nitrogen, and oxygen at solar abundances. We demonstrate that the addition of these metals in the model atmospheres is essential in overcoming the Balmer-line problem, which manifests itself as an inability to fit all the Balmer lines simultaneously with consistent atmospheric parameters. We then present the spectroscopic analysis of our sample of DAO white dwarfs for which we determine the effective temperature, surface gravity, and helium abundance. We also present 18 hot DA white dwarfs that also suffer from the Balmer-line problem. We analyze these stars with models analogous to those for the DAO white dwarfs save for the presence of helium. Systematic differences between our newly determined atmospheric parameters with respect to previous determinations are explored. Far-ultraviolet spectra from the FUSE archive are then examined to demonstrate that there exists a correlation between higher metallic abundances and instances of the Balmer-line problem. The implications of these findings for all hot, hydrogen-rich white dwarfs are discussed. Specifically, the possible evolutionary scenario for DAO white dwarfs is revised and post-extreme horizontal branch evolution is no longer needed to explain the evolution for the majority of the DAO stars. Finally, we discuss how the presence of metals might drive a weak stellar wind which in turn could explain the presence of helium in DAO white dwarfs.

• OSTI ID: 21460101
• Journal Information: Astrophysical Journal, Vol. 720, Issue 1; Other Information: DOI: 10.1088/0004-637X/720/1/581; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ABUNDANCE
BALMER LINES
CARBON
FAR ULTRAVIOLET RADIATION
GRAVITATION
HELIUM
HYDROGEN
LTE
METALS
NITROGEN
OXYGEN
STAR EVOLUTION
STELLAR ATMOSPHERES
STELLAR WINDS
WHITE DWARF STARS
ATMOSPHERES
DWARF STARS
ELECTROMAGNETIC RADIATION
ELEMENTS
EQUILIBRIUM
EVOLUTION
FLUIDS
GASES
NONMETALS
RADIATIONS
RARE GASES
STARS
STELLAR ACTIVITY
ULTRAVIOLET RADIATION